CROSS-REFERENCE TO RELATED APPLICATION
FIELD
[0002] The present subject matter relates to methods for preparing adhesives, and particularly
melt processable adhesives that are polymerized and crosslinked by exposure to actinic
radiation. In many embodiments, the adhesives are produced from controlled architecture
polymers. The present subject matter also relates to adhesive and pre-adhesive compositions,
articles utilizing the adhesives, and systems for processing the adhesives.
BACKGROUND
[0003] UV curable polymeric systems such as various adhesives and coatings are known in
the art. Typically, exposure to UV light for a sufficient duration and intensity results
in crosslinking of the polymer and in certain systems polymerization of monomers or
other species. Curing often results in toughening or hardening of the system.
[0004] Although a wide range of equipment and practices are known for curing polymeric systems,
most if not all are limited in flexibility and/or can only be used in association
with specific polymeric systems having particular curing requirements. Accordingly,
a need exists for new strategies for curing adhesive systems and new adhesive compositions
that can be prepared, stored if desired, and selectively applied or further processed.
SUMMARY
[0005] The difficulties and drawbacks associated with previous approaches are addressed
in the present subject matter as follows.
[0006] In one aspect, the present subject matter provides a method of forming a melt processable
adhesive. The method comprises providing a composition that includes at least one
monomer having one or more ethylenically unsaturated bonds, a first actinic radiation
initiator, and a second actinic radiation initiator, wherein the second initiator
is substantially non-photoactive at activation wavelength(s) of the first initiator.
The method also comprises at least partially polymerizing the composition by exposing
the composition to radiation having wavelengths corresponding to the activation wavelength(s)
of the first initiator. The method additionally comprises at least partially crosslinking
the composition to thereby form the adhesive by exposing the composition to radiation
having wavelengths corresponding to the activation wavelength(s) of the second initiator.
In this method, the composition is free of solvents.
[0007] In another aspect, the present subject matter provides a method of forming an adhesive
by two stages involving exposure to actinic radiation. The method comprises providing
a composition including at least one monomer, a first actinic radiation initiator,
and a second actinic radiation initiator, wherein the second initiator is substantially
non-photoactive at activation wavelength(s) of the first initiator. The method also
comprises at least partially polymerizing the composition by exposing the composition
to radiation having wavelengths corresponding to the activation wavelength(s) of the
first initiator. The method additionally comprises at least partially crosslinking
the composition to thereby form the adhesive by exposing the composition to radiation
having wavelengths corresponding to the activation wavelength(s) of the second initiator.
At least one of the first and the second initiators is a polymer having a photoinitiator
moiety along the polymer backbone.
[0008] In yet another aspect, the present subject matter provides a composition comprising
at least one monomer having one or more ethylenically unsaturated bonds in which the
composition can be readily processed to form an adhesive. The composition also comprises
a first actinic radiation initiator for at least partially polymerizing the at least
one monomer to form a pre-adhesive, the first initiator being activated at a first
activation wavelength(s). The composition additionally comprises a second actinic
radiation initiator for at least partially crosslinking the pre-adhesive, the second
initiator being activated at a second activation wavelength(s) and the second initiator
being substantially non-photoactive at the first activation wavelength(s).
[0009] In still another aspect, the present subject matter provides an acrylate melt processable
pre-adhesive composition comprising at least one acrylate polymer. The composition
also comprises an actinic radiation initiator for at least partially crosslinking
the polymer, the initiator being a photoinitiator moiety along the polymer backbone.
The pre-adhesive composition prior to activation of the initiator exhibits a viscosity
within a range of from 1,000 cps to 80,000 cps at a temperature within a range of
from 110° C to 180° C.
[0010] In yet another aspect, the present subject matter provides an apparatus for polymerizing
and/or crosslinking an adhesive or pre-adhesive composition. The apparatus comprises
a reaction vessel defining an interior chamber and including at least one collar providing
access to the interior chamber. The apparatus also comprises at least one probe assembly
supported by the collar. The probe assembly includes (i) an emitter for emitting light
that polymerizes and/or crosslinks the composition, (ii) a light tube extending from
the emitter and at least partially disposed within the interior chamber of the reaction
vessel, (iii) adjustable positioning provisions for governing position of the light
tube within the interior chamber of the reaction vessel, and (iv) a cover disposed
at a distal end of the light tube, wherein the cover is transparent or substantially
transparent to passage of light emitted from the emitter.
[0011] In still another aspect, the present subject matter provides an apparatus for polymerizing
and/or crosslinking an adhesive or pre-adhesive composition. The apparatus comprises
a reaction vessel defining an interior chamber and at least one sight glass incorporated
in a wall of the vessel and providing visual access to the interior chamber. The apparatus
also comprises at least one probe assembly adjacent the sight glass. The probe assembly
includes an emitter for emitting light that polymerizes and/or crosslinks the composition.
The probe assembly is positioned such that light emitted from the emitter is directed
to the sight glass and passes into the interior chamber of the reaction vessel. The
sight glass is transparent or substantially transparent to passage of light emitted
from the emitter.
[0012] In another aspect, the present subject matter provides an apparatus for polymerizing
and/or crosslinking an adhesive or pre-adhesive composition. The apparatus comprises
a reaction vessel defining an interior chamber, and including mixing provisions having
at least one blade. The apparatus also comprises at least one baffle disposed within
the interior chamber of the reaction vessel. The baffle includes at least one emitter
for emitting light that polymerizes and/or crosslinks the composition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
Figure 1 is a schematic illustration depicting a conventional polymer including various
reactive functional groups and upon exposure to UV radiation, formation of a conventional
randomly crosslinked network.
Figure 2 is a schematic illustration depicting controlled architecture polymers (CAPs)
and upon exposure to UV radiation, formation of enhanced terminally linked networks
in accordance with the present subject matter.
Figure 3 is a schematic illustration of a conventional randomly crosslinked network
and, upon incorporation in an adhesive, typical adhesive properties associated with
such network.
Figure 4 is a schematic illustration of an enhanced terminally linked network and,
upon incorporation in an adhesive, typical adhesive properties associated with such
network in the adhesive in accordance with the present subject matter.
Figure 5 is a process schematic diagram showing a representative process and system
for producing an adhesive in accordance with the present subject matter.
Figure 6 is a schematic flow chart of a method for forming an adhesive in accordance
with the present subject matter.
Figure 7 is a schematic illustration of a tape article including an adhesive in accordance
with the present subject matter.
Figure 8 is a schematic cross sectional view of another tape article in accordance
with the present subject matter.
Figure 9 is a schematic cross sectional view of another tape article in accordance
with the present subject matter.
Figure 10 is a schematic cross sectional view of another tape article in accordance
with the present subject matter.
Figure 11 is a schematic cross sectional view of another tape article in accordance
with the present subject matter.
Figure 12 is a schematic cross sectional view of a sealing or closure assembly including
a region of an adhesive in accordance with the present subject matter.
Figure 13 is a schematic illustration of an embodiment of an apparatus for polymerizing
and/or crosslinking adhesives in accordance with the present subject matter.
Figure 14 is a schematic illustration of another version of an apparatus for polymerizing
and/or crosslinking adhesives in accordance with the present subject matter.
Figure 15 is a schematic illustration of another version of an apparatus for polymerizing
and/or crosslinking adhesives in accordance with the present subject matter.
Figure 16 is a schematic illustration of another version of an apparatus for polymerizing
and/or crosslinking adhesives in accordance with the present subject matter.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0014] The present subject matter relates to methods for preparing adhesives and particularly
actinic radiation polymerizable and crosslinkable melt processable adhesives. In many
embodiments of the present subject matter, the methods are directed to forming adhesives
produced from controlled architecture polymers (referred to as "CAPs" herein). The
present subject matter also relates to adhesives and pre-adhesives formed by the methods
noted herein. The present subject matter also relates to articles containing the adhesives
prepared by the methods described herein. In addition, the present subject matter
relates to equipment and systems for preparing and/or processing the adhesives and
pre-adhesives.
[0015] Before turning attention to the details of the present subject matter and the numerous
embodiments thereof, it is instructive to consider several terms and their definitions
as used herein. The terms "polymerize" or "polymerizing" refer to a process of reacting
monomers together in a chemical reaction to form polymer. And the terms "crosslink"
or "crosslinking" refer to a process of forming bonds that link one polymer chain
to another polymer chain. The bonds may be covalent bonds or ionic bonds. The term
"crosslink" can refer to the bond itself. The terms "cure" and "curing" refer to the
terms "crosslink" or "crosslinking" and are used interchangeably.
[0016] In many embodiments of the present subject matter methods, upon polymerizing and
crosslinking of certain compositions, and particularly those that include CAPs, the
resulting adhesives exhibit enhanced adhesive properties such as relatively high peel
strength and shear strength. These enhanced adhesive properties are believed to at
least partially result from (i) a majority of crosslinking involving functional group(s)
of the polymers being located at or near terminal ends of the polymer chains, and
(ii) an absence or only a minority of crosslinking involving functional group(s) located
within interior regions of the polymer chains. The crosslinked network that results
from the methods as described herein is referred to herein as an "enhanced terminally
linked network" or ETLN. As described in greater detail herein, formation of an ETLN
allows for lower adhesive coatweights, lower viscosities, and better adhesive performance,
among various other advantages and benefits. These and other aspects of the methods,
the CAP based adhesives and ETLNs, and related articles are described in greater detail
herein.
[0017] Although in many embodiments, the present subject matter methods utilize adhesives
including CAPs, it will be appreciated that the present subject matter also includes
methods of polymerizing and crosslinking non-CAP based adhesives. These and other
aspects of the methods, the non-CAP based adhesives polymerized and crosslinked by
such methods, and related articles are described in greater detail herein.
[0018] The present subject matter also provides pre-adhesive compositions that include one
or more monomers which upon polymerization form an adhesive base polymer. The pre-adhesive
composition also includes at least two actinic radiation initiators. In many embodiments
at least one of these initiators, and in particular embodiments both the first and
the second initiators, polymerize with the monomers to form the adhesive. These and
other aspects are described herein.
[0019] The present subject matter also provides a block copolymer composition comprising
at least one of an (AB) diblock copolymer, (ABA) triblock copolymer, an -(AB)
n- multiblock copolymer, and combinations thereof. The present subject matter also
provides a pressure sensitive adhesive derived from a block copolymer composition
comprising at least one of an (AB) diblock copolymer, (ABA) triblock copolymer, an
-(AB)
n- multiblock copolymer, and combinations thereof. The present subject matter further
provides a method of preparing a block copolymer (and/or a method of preparing a pressure
sensitive adhesive derived from a block copolymer composition) comprising at least
one of an (AB) diblock copolymer, (ABA) triblock copolymer, an -(AB)
n- multiblock copolymer, and combinations thereof. The present subject matter also
provides use of a block copolymer (and/or a pressure sensitive adhesive derived from
a block copolymer) composition comprising at least one of an (AB) diblock copolymer,
(ABA) triblock copolymer, an -(AB)
n- multiblock copolymer, and combinations thereof. The block copolymer of the present
subject matter may be an acrylic block copolymer. In other embodiments, the block
copolymer of the present subject matter is preferably an acrylic block copolymer.
Adhesives
[0020] The actinic radiation polymerizable and crosslinkable adhesives of the present subject
matter comprise a melt adhesive or pre-adhesive composition, a first actinic radiation
initiator that in many applications serves to polymerize the adhesive and a second
actinic radiation initiator that is useful for crosslinking the adhesive. In many
embodiments, the second initiator is substantially non-photoactive at activation wavelengths
of the first initiator.
[0021] In many embodiments, the actinic radiation polymerizable and crosslinkable melt adhesive
includes controlled architecture polymers or CAPs. In many embodiments of the present
subject matter, the CAPs are those described in one or more co-pending applications
owned by the Applicant which include
US 2011/0118372;
US 2013/0059971; and
US 2014/0329958. Details of particular embodiment polymers are provided herein. However, it will
be understood that the present subject matter includes the use of any of the polymers
described in these applications.
[0022] In certain embodiments, upon activation of the first initiator to form a pre-adhesive,
the pre-adhesive exhibits a viscosity within a range of from 1,000 cps to 80,000 cps
at a temperature within a range of from 110° C to 180° C. In particular embodiments,
the pre-adhesive exhibits a viscosity within a range of from 30,000 cps to 40,000
cps at a temperature within a range of from 120° C to 140° C. In other embodiments,
the pre-adhesive exhibits a viscosity within a range of from 40,000 cps to 50,000
cps at a temperature within a range of from 120° C to 140° C. And, in still other
embodiments, the pre-adhesive exhibits a viscosity within a range of from 1,000 cps
to 15,000 cps at a temperature within a range of from 110° C to 130° C.
[0023] It will be understood that in no manner is the present subject matter limited to
adhesives or pre-adhesives exhibiting these particular viscosities. It is contemplated
that the present subject matter may also include adhesives or pre-adhesives exhibiting
these viscosities at temperatures less than 110° C, and/or at temperatures greater
than 180° C. Moreover, it is contemplated that the present subject matter may also
provide adhesives or pre-adhesives that exhibit viscosities less than 1,000 cps and/or
greater than 80,000 cps at a wide array of temperatures.
[0024] The present subject matter adhesives and/or pre-adhesive compositions comprise two
or more actinic radiation initiators and in particular embodiments two or more UV
activated initiators. Although not wishing to be bound by any particular theory, it
is believed that in many embodiments of the present subject matter, one or both initiator(s),
when irradiated with actinic radiation and particularly UV light, is excited to a
higher energy state and abstracts a hydrogen atom from a functional group on the polymer,
thereby generating a free radical that is available for further reaction, such as
for example free radical addition crosslinking with another polymer chain or functional
group on the polymer. However, it will be understood that the present subject matter
includes the use of nearly any type of initiator and is not limited to those that
abstract hydrogen atoms. For example, a variety of initiators are known that decompose
or cleave into free radicals upon exposure to light, and more particularly UV radiation.
[0025] A variety of initiators are known and can potentially be incorporated in the present
subject matter adhesives, including benzophenone, acetophenone, acyl phosphine, thioxanthone,
derivatives of these compounds, and similar compounds. Each compound functions as
a photoinitiator by absorbing energy within the UV region of the electromagnetic spectrum.
[0026] Several types of photoinitiators that absorb in the near UV region of the spectrum
are known, including acylphosphine oxide-type photoinitiators, redshifted benzophenone-type
photoinitiators, and thioxanthone-type photoinitiators. Many of these may be suitable
for use with the present subject matter compositions.
[0027] Commercially available acylphosphine oxide-type photoinitiators include "Lucirin
TPO" (2,4,6-trimethylbenzoyldiphenylphosphine oxide) and "Lucirin TPO-L" (liquid),
sold by BASF, and "BAPO" (bis 2,6-dimethoxybenzoyl!-2,4-trimethylpentylphosphine oxide),
sold by Ciba.
[0028] The so-called "redshifted benzophenone-type photoinitiators" are benzophenone derivatives
in which one or more hydrogen atoms is replaced by a functional group or groups which
cause a redshift (towards longer wavelengths) in the UV absorption spectrum of the
molecule, as compared to the UV absorption spectrum of benzophenone. An example is
"QUANTACURE BMS" (4-benzoyl-4'-methyldiphenylsulfide).
[0029] Commercially available thioxanthone-type photoinitiators include "Quantacure ITX,"
which is believed to be a mixture of 2-isopropyl- and 4-isopropylthioxanthone isomers.
[0030] Other suitable photoinitiators can be identified by those skilled in the art and
utilized in the present subject matter. Moreover, if the adhesive is compounded without
a pigment, photoinitiators that absorb at shorter UV wavelengths can be employed,
including less expensive, simpler photoinitiators such as unsubstituted acetophenone,
benzil, benzophenone, quinone, and thioxanthone.
[0031] Combinations of any of the noted photoinitiators can potentially be used for the
first initiator, the second initiator, and/or both initiators.
[0032] In certain embodiments of the present subject matter, particular initiators are used
which are in the form of polymerizable monomers. During formation of the polymer(s)
of the adhesives, the first and/or second initiators are incorporated in the adhesive
polymers and can be subsequently activated by UV irradiation. Thus, at least one of
the first and second initiators is polymerizable with the monomers that form the adhesive
and/or its polymers. In these embodiments, the first initiator is a polymerizable
photoinitiator and initiates polymerization of the monomers that form the adhesive.
Polymerization of the monomers may be initiated either directly or indirectly via
sensitization, synergists, or co-initiator mechanisms. Nonlimiting examples of polymerizable
photoinitiators include acyl phosphines, thioxanthone derivatives, camphorquinone
and/or related derivatives, and combinations thereof. Examples of acyl phosphines
include TPO, TPO-L, and BAPO. However, it will be understood that the present subject
matter includes other agents that absorb UV radiation and which may be suitable for
use as the first initiator. For example, it is contemplated that the UV absorbing
material can be in the form of a distinct agent that is added to the system, bound
to a polymer, or formed in-situ by an association of materials or agents in the system.
This latter strategy is referred to herein as a "photoinitiator free" technique and
can be based upon complexes such as a charge transfer complex or a donor-acceptor
complex.
[0033] In these embodiments, the second initiator is in the form of a polymerizable monomer
having a photoinitiator moiety attached or coupled thereto. Generally, the polymerizable
monomer can be any monomer suitable for forming the polymeric matrix of the adhesive
system. Nonlimiting examples of such monomers include acrylate and methacrylate monomers.
Additional examples of potentially suitable monomers are described herein.
[0034] The photoinitiator moiety of this version of the second initiator must not be appreciably
photoactive at wavelengths at which the first initiator activates. Thus, the photoinitiator
moiety is generally inactive at the activation wavelengths of the first initiator.
[0035] Generally, the photoinitiator moiety of the polymerizable monomer version of the
second initiator is a hydrogen abstractor type initiator. For example, the moiety
may include a derivative of benzophenone. However, the present subject matter includes
cleavage type photoinitiators. Furthermore, the present subject matter includes activation
via sensitizers, co-initiators, and/or synergists. As previously described for the
first polymerizable initiator, the second initiator in the form of a polymerizable
monomer having a photoinitiator moiety can be in the form of a distinct agent that
is added to the system, bound to a polymer, or formed in-situ by an association of
materials or agents in the system in a photoinitiator-free technique such as based
upon complexes such as a charge transfer complex or a donor-acceptor complex.
[0036] As noted, in many embodiments the adhesives utilize a first initiator and a second
initiator which are activated at different wavelengths. This enables activation of
the first initiator without activating the second initiator. The initiators are both
activated by actinic radiation and in many embodiments by UV radiation, i.e., electromagnetic
radiation having a wavelength in a range of from about 100 nm to about 500 nm. In
certain embodiments, the first initiator is activated at wavelengths within a range
of from 200 nm to 500 nm, particularly from 300 nm to 500 nm, and more particularly
from 350 nm to 500 nm. And, the second initiator is activated at wavelengths within
a range of from 100 nm to 400 nm, particularly from 200 nm to 400 nm, and more particularly
from 200 nm to 375 nm. Generally, the wavelength(s) at which the first initiator is
activated is (are) different from those at which activation occurs for the second
initiator.
[0037] Thus, in many versions of the present subject matter, one or both of the first and
second initiators is/are in the form of a polymer having a photoinitiator moiety along
the polymer backbone. And, in certain embodiments, one or both of the first and second
initiators is/are in the form of polymerizable monomers and/or oligomers having a
photoinitiator moiety.
[0038] The first and/or second initiators can also be activated by exposure to electron
beam radiation. It is also contemplated that one initiator can be activated by exposure
to UV radiation and another initiator can be activated by exposure to electron beam
radiation.
[0039] The total amount of initiators added to the polymer in preparing the adhesive depends
on several factors, including the amount of pigment and/or other agents added, the
coat weight (thickness) of the adhesive on the substrate, the web speed during curing,
and the type and cost of the initiators used. In many embodiments, the initiator is
the most expensive ingredient in the adhesive. Therefore, ordinarily it is desirable
to minimize the amount of initiator added to the polymer, so long as enough initiator
is included to achieve the desired end properties of the resulting composition.
[0040] In certain embodiments of the present subject matter, a pigment or other coloring
agent(s) is added to the composition, typically prior to crosslinking, in order to
render the adhesive opaque, and/or to impart color to the adhesive. Opaque pigments
such as for example titanium dioxide typically are added by the coating industry precisely
because of their high hiding power. However, their presence generally interferes with
UV initiated crosslinking of the adhesive polymer. In the present subject matter,
however, initiators that absorb in the near UV region of the spectrum can be employed
with pigmented (as well as non-pigmented) formulations, thereby avoiding interference
with UV initiated crosslinking of the adhesive.
[0041] The amount of pigment added to the compounded polymer in a given formulation, like
the amount of initiator, depends on a number of factors, including the desired degree
of opacity, desired degree of cure, whether other fillers are present, the type and
amount of photoinitiator present, and cost considerations.
[0042] For the present subject matter, where pigmented adhesive compositions are utilized,
UV initiated crosslinking can be facilitated by decreasing the amount of titanium
dioxide present (or other pigment) and/or increasing the amount of initiator. As a
practical matter, though, pigment loadings above about 15 parts pigment per hundred
parts polymer (or, if the copolymer is tackified, about 15 parts pigment per 100 parts
polymer plus tackifier) are less preferred than lower pigment loadings. UV initiated
crosslinked, pressure sensitive adhesive compositions having high cohesive strength
can be prepared in accordance with the present subject matter with higher pigment
loadings, but require higher (and more expensive) initiator concentrations and/or
longer crosslinking times.
[0043] In some embodiments, the adhesive composition is formulated with a colored (non-white)
pigment.
[0044] Generally, yellow and red pigments do not substantially interfere with photoinitiators
that absorb in the UV region. Hence, adhesives compounded with such pigments can be
UV crosslinked to a high cohesive strength by using UV-activatable, photoinitiators.
Blue pigments tend to absorb strongly in at least part of the near UV region. By minimizing
the amount of blue pigment that is added, however, UV crosslinked adhesives can be
prepared in the manner described herein.
[0045] In addition to the pigment and initiator(s), in some embodiments, the polymer is
further compounded with a tackifier. In certain embodiments such as if the adhesive
is a pressure sensitive adhesive, tackifier may be added to improve the tack of the
pressure sensitive adhesive.
[0046] A variety of tackifiers, many of which are well known in the industry, can potentially
be used in the practice of the present subject matter. Representative, nonlimiting
examples of such tackifiers include hydrocarbon resins and rosin resins. Such tackifiers
include, but are not limited to, rosins and rosin derivatives including rosinous materials
that occur naturally in the oleoresin of pine trees, as well as derivatives thereof
including rosin esters, modified rosins such as fractionated, hydrogenated, dehydrogenated,
and polymerized rosins, modified rosin esters and the like. Generally, up to about
45 parts tackifier per hundred parts polymer are added. However, it will be appreciated
that the present subject matter includes the use of lesser amounts and/or greater
amounts of tackifiers.
[0047] A wide range of tackifiers are commercially available including, but not limited
to, Foral® 85 (glycerol ester of a highly stabilized rosin), Foral® 105 (pentaerythritol
ester of a hydrogenated rosin), Stabilite ester 10, and Pentalyn® H, manufactured
and sold by Hercules, Inc., PE Estergum and the like, manufactured by Arizona Chemical
Co., and Sylvatac® 40N, Sylvatac® RX, Sylvatac® 95 and the like, manufactured by Sylvachem
Corporation.
[0048] There may also be employed as tackifiers terpene resins which are hydrocarbons of
the formula C10H16, occurring in most essential oils and oleoresins of plants, and
phenol modified terpene resins like alpha pinene, beta pinene, dipentene, limonene,
myrecene, bornylene, camphene, and the like. Various aliphatic hydrocarbon resins
like Escorez™ 1304, manufactured by Exxon Chemical Co., and aromatic hydrocarbon resins
based on C9's, C5's, dicyclopentadiene, coumarone, indene, styrene, substituted styrenes
and styrene derivatives and the like can also be used.
[0049] Hydrogenated and partially hydrogenated resins such as Regalrez™ 1018, Regalrez™
1033, Regalrez™ 1078, Regalrez™ 1094, Regalrez™ 1126, Regalrez™ 3102, Regalrez™ 6108,
etc., produced by Hercules Corporation, can be used as tackifiers in the present subject
matter as well. Various terpene phenolic resins of the type SP 560, manufactured and
sold by Schenectady Chemical Inc., Nirez 1100, manufactured and sold by Reichold Chemical
Inc., and Piccolyte® S-100, manufactured and sold by Hercules Corporation, are particularly
useful tackifiers for the present subject matter. Further, various mixed aliphatic
and aromatic resins, such as Hercotex AD 1100, manufactured and sold by Hercules Corporation,
can also be used as tackifiers.
[0050] Additionally, the melt processable, actinic radiation polymerizable and crosslinkable
adhesive compositions may comprise one or more inhibitors. A viable free radical scavenger
may be present to prevent premature gelation, either in storage or preparation for
coating, especially in the case of hot melt adhesive compositions. Inhibitors comprising
phenolic compounds are one class of such materials that may be used in the present
subject matter, including, for example, 4-methoxyphenol (MEHQ, methyl ether of hydroquinone),
hydroquinone, 2-methylhydroquinone, 2-t-butylhydroquinone, t-butyl catechol, butylated
hydroxy toluene, and butylated hydroxy anisole and the like and combinations thereof.
Other inhibitors that may be used include phenothiazine and anaerobic inhibitors,
such as the NPAL type inhibitors (tris-(N-nitroso-N-phenylhydroxylamine) aluminum
salt) from Albemarle Corporation, Baton Rouge, La. Combinations of inhibitors may
be used.
[0051] The adhesives of the present subject matter may further comprise one or more conventional
adjuvants such as fillers, plasticizers, diluents, and the like. Combinations of one
or more of these components can be used including combinations with pigment(s) and/or
tackifier(s). If desired, diluents such as plasticizers may be added in the place
of a portion of the tackifier in order to alter the properties of tackiness and cohesive
strength.
[0052] Generally, the melt processable, actinic radiation polymerizable and crosslinkable
adhesives include at least 95% solids, in many embodiments at least 98% solids, in
particular embodiments at least 99% solids, and in certain versions at least 99.5%
solids.
Controlled Architecture Polymers (CAPs)
[0055] In particular embodiments, the melt processable, actinic radiation polymerizable
and crosslinkable adhesives of the present subject matter are produced from controlled
architecture polymers. In many embodiments the polymers are acrylic polymers.
[0056] In many embodiments of the present subject matter, the melt processable, actinic
radiation polymerizable and crosslinkable adhesives that include controlled architecture
polymers have one or more reactive functional groups incorporated in select blocks
or regions of the polymer at designated concentrations within those regions. As noted,
in many embodiments the polymers are acrylic polymers. The reactive functional groups
can be incorporated in the polymers by one or more polymerizable monomers as described
herein. Thus, a polymerizable monomer and/or comonomer as described herein may constitute
one or more reactive functional groups. The present subject matter additionally provides
adhesives utilizing the controlled architecture polymers.
[0057] Generally, the CAPs comprise at least two blocks or regions different from one another,
located anywhere along the polymer backbone or chain, or elsewhere within the polymer.
Thus, a CAP as described herein may contain one or more A blocks, one or more B blocks,
and one or more C blocks anywhere within the polymer. The preferred polymers may comprise
other types of blocks or regions such as D blocks, E blocks ... etc. In a preferred
aspect, particular amounts of reactive functional groups are provided in association
with at least two of the blocks, referred as blocks A and B for purposes of convenience.
And, in a more preferred aspect, the amounts of reactive functional groups are controlled
in the blocks A and B such that the total amount of a reactive functional group is
distributed between two blocks, for example blocks A and B, within a certain range
of weight ratios. Generally, this ratio is referred to herein as an "apportionment
ratio" and is defined as the ratio of the weight percent of a reactive functional
group associated with block A to the weight percent of the reactive functional group
associated with block B. Generally, a useful range of ratios, i.e. apportionment ratios,
for the controlled architecture polymers described herein is from about 1.1:1 to about
10,000:1. In many embodiments, the apportionment ratios of the ordered polymers are
from 1.1:1 to 1,000:1, or from 1.1:1 to 100:1. In other embodiments, the apportionment
ratios of the ordered polymers are from 6:1 to 10,000:1, or from 6:1 to 1,000:1, or
from 6:1 to 100:1, or from 6:1 to 80:1. However, it will be appreciated that the present
subject matter includes polymers with one or more reactive functional groups distributed
between polymeric blocks at apportionment ratios less than or greater than these ranges.
For example, the present subject matter includes polymers as described herein however
having apportionment ratios in excess of 10,000:1, such as for example about 50,000:1,
about 75,000:1, and about 100,000:1.
[0058] The CAPs are preferably formed from (i) monomers of acrylates and/or methacrylates
and (ii) polymerizable acrylate comonomers having one or more reactive functional
groups. The term "monomer" or "comonomer" as used herein refers to a molecule, starting
unit, or chemical species that can bond together to form a polymer. The term also
includes a repeating unit within the polymer. As noted, these monomers or comonomers
are generally referred to herein as blocks or regions such as "A", "B", and/or "C".
The acrylate monomers include C1 to about C20 alkyl, aryl or cyclic acrylates such
as methyl acrylate, ethyl acrylate, phenyl acrylate, butyl acrylate, 2-ethylhexyl
acrylate, isobornyl acrylate and functional derivatives of these acrylates such as
2-hydroxy ethyl acrylate, 2-chloro ethyl acrylate, and the like. These monomers or
comonomers typically contain from about 3 to about 20 carbon atoms, and in one embodiment
about 3 to about 8 carbon atoms. The methacrylate monomers include C1 to about C20
alkyl, aryl or cyclic methacrylates such as methyl methacrylate, ethyl methacrylate,
butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, isobornyl methacrylate,
and functional derivatives of these methacrylates such as 2-hydroxyethyl methacrylate,
2-chloroethyl methacrylate, and the like. These monomers or comonomers typically contain
from about 4 to about 20 carbon atoms, and in one embodiment about 4 to about 8 carbon
atoms. Combinations of acrylates and methacrylates can also be used.
[0059] Although in many embodiments the CAPs preferably comprise (i) monomers of acrylates
and/or methacrylates, and (ii) polymerizable acrylate comonomers, i.e. blocks A and
B, the present subject matter includes the use of additional and/or different monomers
as blocks in the polymer. Nearly any free radically polymerizable monomer or combination
of monomers could be used as blocks A, B, C, D, E, etc. in the controlled architecture
polymers described herein. Accordingly, it will be understood that in no way is the
present subject matter limited to the CAPs including acrylate and/or methacrylate
blocks.
[0060] The polymerizable monomers and comonomers can include as reactive functional groups
acrylonitrile groups, acrylamide groups, methacrylamide groups, vinyl ester groups,
vinyl ether groups, vinyl amide groups, vinyl ketone groups, styrene groups, halogen-containing
groups, ionic groups, acid-containing groups, base-containing groups, olefin groups,
silane groups, epoxy groups, hydroxyl groups, anhydride groups, and mixtures of two
or more groups thereof. It is also contemplated to include silyl groups, carboxyl
groups, carbonyl groups, carbonate ester groups, isocyanato groups, amino groups,
amide groups, imide groups, mercapto groups, and acetoacetyl groups in any combination
and/or in combination with one or more of any of the previously noted groups.
[0061] The acrylonitrile groups can include acrylonitrile and alkyl substituted acrylonitriles.
The alkyl groups typically contain from 1 to about 20 carbon atoms, and in one embodiment
from 1 to about 10 carbon atoms, and in another embodiment from 1 to about 5 carbon
atoms. Examples include methacrylonitrile and ethacrylonitrile.
[0062] The acrylamide groups can include acrylamide and its derivatives including the N-substituted
alkyl and aryl derivatives thereof. These include N-methyl acrylamide, N,N-dimethyl
acrylamide, t-octyl acrylamide, N-aminoethyl acrylate, N-aminoethyl methacrylate,
and the like.
[0063] The methacrylamide groups can include methacrylamide and its derivatives including
the N-substituted alkyl and aryl derivatives thereof.
[0064] The vinyl ester groups can include vinyl acetate, vinyl propionate, vinyl butyrate,
vinyl valerate, vinyl versitate, vinyl isobutyrate, and the like.
[0065] The vinyl ether groups can include vinyl ethers having 1 to about 8 carbon atoms
including ethylvinyl ether, butylvinyl ether, 2-ethylhexylvinyl ether, and the like.
[0066] The vinyl amide groups can include vinyl amides having 1 to about 8 carbon atoms
including vinyl pyrrolidone, and the like.
[0067] The vinyl ketone groups can include vinyl ketones having 1 to about 8 carbon atoms
including ethylvinyl ketone, butylvinyl ketone, and the like.
[0068] The styrene groups can include styrene, indene, and substituted styrenes represented
by the formula (I):
wherein each of A, B, C, D, E and F is independently selected from hydrogen, C1 to
about C4 alkyl or alkoxy groups (especially methyl or methoxy groups,) halogroups
(especially chloro), thio, cyano, carboxylic acid or ester, or fluorinated alkyl groups
of 1 to about 4 carbon atoms. Examples include methyl styrene (sometimes referred
to as vinyl toluene), alpha-methyl styrene, divinylbenzene, chlorostyrene, chloromethyl
styrene, and the like.
[0069] The halogen-containing groups can include vinyl chloride, vinyl bromide, vinyl fluoride,
vinylidene chloride, vinylidene bromide, vinylidene fluoride, halogen substituted
propylene monomers, and the like, with vinyl bromide and vinylidene chloride being
preferred.
[0070] The ionic groups can include sodium vinyl sulfonate, sodium styrene sulfonate, sodium
methallyl sulfonate, sodium acrylate, sodium methacrylate, and the like, with sodium
vinyl sulfonate, sodium styrene sulfonate and sodium methallyl sulfonate being preferred.
[0071] The acid-containing groups can include unsaturated carboxylic acids containing from
3 to about 20 carbon atoms. Preferred groups include acrylic acid, methacrylic acid,
vinyl sulfonic acid, itaconic acid, beta carboxyl ethyl acrylate, mono-2-acroyloxypropyl
succinate, and the like.
[0072] The base-containing groups can include vinyl pyridine and the like.
[0073] The olefin groups can include isoprene, butadiene, C2 to about C8 straight chained
and branched alpha-olefins such as ethylene, propylene, butylene, isobutylene, diisobutylene,
4-methyl pentene-1, 1-butene, 1-hexene, 1-octene, and the like.
[0074] The silane groups can include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane,
vinylmethyldimethoxysilane, vinylmethyldiethoxy-silane, vinylmethyldipropoxysilane,
γ-methacryloxypropyl-trimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyl-tripropoxysilane,
γ-methacryloxydimethoxysilane, γ-methacryloxypropyl-methyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane,
γ-methacryl-oxypropylmethyldipropoxysilane, γ-methacryloxymethyl-dimethoxysilane,
γ-methacryloxymethyltrimethoxysilane, γ-methacryloxymethyltriethoxy-silane, (methacryloxymethyl)
methyldimethoxysilane, (methacryloxymethyl)-methyldiethoxysilane, γ-methacryloxypropyltriacetoxysilane,
γ-acηloxypropyltrimethoxy-silane, γ-acryloxypropyltriethoxy-silane, γ-methacηl-oxymethyldiethoxysilane,
γ-acryloxypropyltripropoxy-silane, γ-acryloxypropyl-methyldimethoxysilane, γ-acryloxypropylmethyldiethoxysilane,
γ-acryloxypropylmethyldipropoxysilane, and the like.
[0075] The epoxy groups can include for example, glycidyl methacrylate and glycidal acrylate.
[0076] The hydroxyl groups can include for example hydroxy ethyl acrylate, hydroxyl ethyl
methacrylate, hydroxyl isopropyl acrylates, hydroxyl isopropyl methacrylate, hydroxyl
butyl acrylate, hydroxyl butyl methacrylate and the like.
[0077] The anhydride groups can include for example maleic anhydride, itaconic anhydride,
citraconic anhydride and the like.
[0078] In addition to the monomer having functional group(s), the reactive segment may include
at least one monomer having the formula (II):
where R
3 is H or CH
3 and R
4 is a branched or unbranched, saturated alkyl group having 4 to 14 carbon atoms. The
reactive segment may instead or additionally include at least one monomer having the
formula (III):
where R is H or CH
3 and X represents or contains a functional group capable of crosslinking.
[0079] Representative preferred reactive functional groups for incorporating in the polymers
described herein include, but are not limited to, acrylic acid, 2-methacryloxyethylphthalic
acid (PAMA), and combinations thereof. It will be appreciated that a wide array of
other reactive functional groups can be used instead of or in conjunction with any
of these reactive functional groups.
[0080] The CAPs may exhibit particular distributions of reactive functional groups throughout
the polymer. The distribution of each type of reactive functional group incorporated
into a polymer can be expressed in terms of a weight ratio of the weight percent amount
of that reactive functional group in one block or region, i.e. block A, and the weight
percent amount of that reactive functional group in another block or region, i.e.
block B. As noted, this weight ratio is referred to herein as the apportionment ratio.
For many applications of interest, it is preferred to incorporate greater amounts
of reactive functional groups in an A block of a polymer as compared to amounts of
reactive functional groups in a different block, i.e. a B block. Therefore, by strategically
locating particular blocks having certain weight percentages of specified reactive
functional groups within a polymer, precise polymeric architectures can be produced,
each with desired loading and placement of functional groups within the polymer. This
strategy enables the formation of polymers having particular blocks located at desired
regions within the polymer, and the resulting polymer having particular concentrations
of functional groups within the desired regions. For example, it may be desired to
produce a polymer having a certain combination of blocks, e.g. A, B, and C, and for
such polymer to exhibit a relatively high concentration of functional groups within
the end regions or other locations of the polymer as compared to other regions such
as the interior of the polymer.
[0081] The present subject matter is applicable to a wide array of polymer sizes and weights.
Typically, the present subject matter is applicable to polymers having a molecular
weight of from about 10,000 to about 300,000, preferably from about 50,000 to about
200,000, and most preferably from about 100,000 to about 150,000 g/mol. However, it
will be understood that in no way is the present subject matter limited to these molecular
weights. It will be appreciated that these molecular weights for the noted polymers
are average molecular weights and unless indicated otherwise, are weight average molecular
weights.
[0082] In certain embodiments, the polymers exhibit relatively narrow ranges of molecular
weight and thus have relatively low polydispersity values. Typically, the preferred
embodiment polymers exhibit polydispersity (Pdi) values of less than 4.0, preferably
less than 3.5, more preferably less than 3.0, more preferably less than 2.5, and most
preferably less than 2.0. In certain embodiments, the preferred embodiment polymers
exhibit polydispersities of less than 1.5, and as low as about 1.4.
[0083] As previously noted, it will also be understood that the CAPs may include two or
more different types of reactive functional groups. Thus, different reactive functional
groups can be incorporated into one or more end region(s) and/or into one or more
interior regions of the polymer(s) of interest. Therefore, a polymer of the present
subject matter can include 1, 2, 3, or more different reactive functional groups.
And, each group can be defined as apportioned along the polymer in a particular ratio
as described herein. For example, a CAP can include a first reactive functional group
apportioned between blocks A and B at a first apportionment ratio, and a second reactive
functional group apportioned between blocks A and B at a second apportionment ratio
different from the first apportionment ratio. Moreover, it is also contemplated that
the second reactive functional group or a third reactive functional group could be
apportioned between one of blocks A and B, and another block, block C. Alternatively,
the second or third reactive functional group could be apportioned between a set of
blocks different from blocks A and B, such as blocks C and D.
[0084] Representative and non-limiting examples of ranges of glass transition temperatures
(Tg) for the controlled architecture polymers typically are from about -60° C to about
-35° C. However, it will be appreciated that the polymers of the present subject matter
can exhibit Tg's outside of this range such as less than -60° C and/or greater than
-35° C.
[0085] In certain embodiments, the present subject matter utilizes a two-step polymerization
process for making a crosslinkable acrylic copolymer having a first segment with reactive
functional groups provided by at least one acrylic monomer. A second segment is added
to the first segment to form the acrylic copolymer. The second segment does not contain
crosslinkable functional groups and is miscible with the first segment.
[0086] The reactive segment of the acrylic polymer may be a copolymer derived from one or
more of the monomers of the non-reactive segment and at least one polymerizable comonomer
having crosslinkable functionality. In one embodiment, the reactive segment comprises
at least one monomer having the formula:
where R is H or CH
3 and X represents or contains a functional group capable of crosslinking. The crosslinkable
functional group of the reactive segment of the acrylic polymer is not particularly
restricted, but may include one or more crosslinkable silyl, hydroxyl, carboxyl, carbonyl,
carbonate ester, isocyanato, epoxy, vinyl, amino, amide, imide, anhydride, mercapto,
acid, acrylamide and acetoacetyl groups.
[0087] Hydroxy functional monomers include, for example, hydroxyl ethyl (meth)acrylate,
hydroxyl isopropyl (meth)acylate, hydroxyl butyl (meth)acrylate and the like. Epoxy
functional monomers include, for example, glycidyl methacrylate and glycidal acrylate.
[0088] The acid containing monomers include unsaturated carboxylic acids containing from
3 to about 20 carbon atoms. The unsaturated carboxylic acids include, among others,
acrylic acid, methacrylic acid, itaconic acid, beta carboxy ethyl acrylate, mono-2-acroyloxypropyl
succinate, and the like. Anhydride containing monomers include maleic anhydride, itaconic
anhydride, citraconic anhydride and the like.
[0089] The acrylamides include acrylamide and its derivatives including the N-substituted
alkyl and aryl derivatives thereof. These include N-methyl acrylamide, N,N-dimethyl
acrylamide, t-octyl acrylamide and the like. The methacrylamides include methacrylamide
and its derivatives including the N-substituted alkyl and aryl derivatives thereof.
The vinyl esters include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate,
vinyl versitate, vinyl isobutyrate and the like. The vinyl ethers include vinyl ethers
having 1 to about 8 carbon atoms including ethylvinyl ether, butylvinyl ether, 2-ethylhexylvinyl
ether and the like. The vinyl amides include vinyl amides having 1 to about 8 carbon
atoms including vinyl pyrrolidone, and the like. The vinyl ketones include vinyl ketones
having 1 to about 8 carbon atoms including ethylvinyl ketone, butylvinyl ketone, and
the like.
[0090] The polymerizable silanes include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane,
vinylmethyldimethoxysilane, vinylmethyldiethoxy-silane, vinylmethyldipropoxysilane,
γ-methacryloxypropyl-trimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyl-tripropoxysilane,
γ-methacryloxydimethoxysilane, γ-methacryloxypropyl-methyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane,
γ-methacryl-oxypropylmethyldipropoxysilane, γ-methacryloxymethyl-dimethoxysilane,
γ-methacryloxymethyltrimethoxysilane, γ-methacryloxymethyltriethoxy-silane, (methacryloxymethyl)
methyldimethoxysilane, (methacryloxymethyl)-methyldiethoxysilane, γ-methacryloxypropyltriacetoxysilane,
γ-acryloxypropyltrimethoxy-silane, γ-acryloxypropyltriethoxy-silane, γ-methacryl-oxymethyldiethoxysilane,
γ-acryloxypropyltripropoxy-silane, γ-acryloxypropyl-methyldimethoxysilane, γ-acryloxypropylmethyldiethoxysilane,
γ-acryloxypropylmethyldipropoxysilane, and the like.
[0091] In addition to the monomer having functional group(s), the reactive segment may include
at least one monomer having the formula:
where R
3 is H or CH
3 and R
4 is a branched or unbranched, saturated alkyl group having 4 to 14 carbon atoms.
[0092] In one embodiment, the reactive segments include about 40% to about 99% by weight
of the one or more monomers of the non-reactive segments. In another embodiment, the
reactive segments include about 50% to about 99% by weight of the one or more monomers
of the non-reactive segments. In another embodiment, the reactive segments include
about 60% to about 99% by weight of the one or more monomers of the non-reactive segments.
In another embodiment, the reactive segments include about 70% to about 99% by weight
of the one or more monomers of the non-reactive segments. In another embodiment, the
reactive segments include about 80% to about 99% by weight of the one or more monomers
of the non-reactive segments. In another embodiment, the reactive segments include
about 90% to about 99% by weight of the one or more monomers of the non-reactive segments.
In another embodiment, the reactive segments include less than about 40% by weight
of the one or more monomers of the non-reactive segments. In another embodiment, the
reactive segments include more than about 99% by weight of the one or more monomers
of the non-reactive segments.
[0093] As used herein, the term "molecularly miscible" means a compound or mixture of compounds
that exhibit properties in the bulk state that can be observed and/or measured by
one of ordinary skill in the art and are indicative of single phase behavior. The
term "single phase behavior" refers to behavior or physical properties that are uniform
or substantially so. With respect to the acrylic copolymer, the observation of a single
Tg is indicative of polymer segment miscibility. The single Tg is intermediate between
those of the constituent polymer segments and varies monotonically between these values
as the relative amounts of each segment changes. In contrast to single phase behavior
evidenced by a molecularly miscible compound or mixture of compounds, at a given temperature,
a phase separated compound demonstrates multiple, independent sets of properties that
are attributable to the different phases of matter present therein. Such sets of properties
include, without limitation, T
g, solubility parameters, refractive index, and physical state/phase of matter. Accordingly,
the term "phase separated" is defined as two or more substances which are molecularly
segregated due to one or more chemical and/or physical properties dependent upon,
without limitation, polarity, molecular weight, relative amounts of the polymer segments,
and T
g (phase of matter).
[0094] Evidence of immiscibility/incompatibility between blocks/segments of a block copolymer,
such as an ABA block copolymer, can be confirmed via rheological measurements such
as Dynamic Mechanical Analysis (DMA) or Differential Scanning Calorimetry (DSC) and
the microstructure determined from microscopy. Miscible polymers exhibit no heterogeneity
(i.e., are single phase polymers) in their microstructure. The degree of miscibility/compatibility
of a polymer blend can be simply determined by measuring the glass transition temperature(s)
in a DMA or DSC can. The presence of two Tgs indicates immiscibility, while the presence
of only a single Tg indicates a miscible blend. For block copolymers with mutually
incompatible blocks, the microdomains formed by the different blocks exhibit separate/different
Tgs, and for incompatible block copolymers separate Tg values are also observed in
the DMA and/or DSC plots. For example, for typical styrenic and acrylic ABA block
copolymers, the hard A block and the soft B block have sufficiently different solubility
parameters such that they are not thermodynamically compatible with each other. As
a result, block copolymer-based adhesives have a unique microphase- separated morphology,
where A blocks form a hard phase embedded in a soft, continuous phase composed of
B blocks. That is, a result of the frequent immiscibility/incompatibility of the two
types of blocks present in ABA block copolymers, block copolymers generally exhibit
two distinct glass transitions (a DMA bimodal tan δ curve) at temperatures very close
to those of the corresponding homopolymers. The presence of acid, however, in block
copolymers such as P(MMA/MAA)-PBA-P(MMA/MAA) raises the Tg of the end block and also
enhances the phase separation between the soft acrylate and the hard PMMA domains.
Therefore, block copolymers can exhibit morphologies which range from two-phase segregated
materials to single-phase homogeneous materials.
[0096] In many embodiments of the present subject matter the CAPs utilized in the adhesives
exhibit particular distributions of reactive functional groups within the polymer.
In various embodiments, at least 80% of the reactive functional groups are located
within the end blocks or terminal ends of the polymer. For purposes of this disclosure,
the terms "end blocks" or "terminal blocks" of the polymer refer to end segments of
the polymer. These end blocks or terminal ends have a molecular weight less than 50,000
g/mol; in particular embodiments, the molecular weight may be less than 30,000 g/mol,
while in still additional particular embodiments, the molecular weight of the end
blocks may be less than 10,000 g/mol.
[0097] The remaining portion of the reactive functional groups, i.e., up to 20%, are located
within one or more interior region(s) of the polymer. In particular embodiments, at
least 90% of the reactive functional groups are located within the end blocks or terminal
ends and the remaining portion, i.e., up to 10%, is located within one or more interior
regions of the polymer. In still other embodiments, at least 95% of the reactive functional
groups are located within the end blocks or terminal ends of the polymer. The remaining
portion of the reactive functional groups, i.e., up to 5%, are located within one
or more interior region(s) of the polymer. And in specific embodiments, at least 99%
of the reactive functional groups are located within the end blocks or terminal ends
and the remaining portion, i.e., up to 1%, is located within one or more interior
regions of the polymer.
[0098] As previously noted, upon crosslinking of the present subject matter adhesives and
formation of an enhanced terminally linked polymeric network, the resulting enhanced
adhesive exhibits certain properties that are at least comparable to, and in many
instances superior to, those of adhesives utilizing conventional randomly crosslinked
polymeric networks. Figure 1 is a schematic illustration depicting a conventional
polymer including various reactive functional groups and upon exposure to UV radiation,
formation of a conventional randomly crosslinked network. In Figure 1, the various
functional groups are schematically represented by the vertical line segments located
along the polymer chain or backbone which is represented by the horizontal line segment.
Upon crosslinking, crosslink bonds involve interior regions of the polymers as a result
of many functional groups being located within those interior regions. Figure 2 is
a schematic illustration depicting controlled architecture polymers (CAPs) and upon
exposure to UV radiation, formation of an enhanced terminally linked network in accordance
with the present subject matter. The CAPs include various functional groups located
primarily at or near terminal ends of the polymers. Thus, upon crosslinking, the network
that forms is characterized by crosslink bonds primarily at terminal ends of the polymers,
and an absence or a relatively minor extent of crosslink bonds involving interior
regions of the polymers.
[0099] The resulting polymeric networks influence and in many regards determine physical
properties of the resulting adhesives. Figure 3 is a schematic illustration of a conventional
randomly crosslinked network and, upon incorporation in an adhesive, typical adhesive
properties associated with such network. Figure 4 is a schematic illustration of an
enhanced terminally linked network and, upon incorporation in an adhesive, typical
adhesive properties associated with such network in the adhesive in accordance with
the present subject matter. While the graphs in Figures 3 and 4 do not contain values
on the y-axis, each graph is presented with the same scale. Accordingly, the networked
polymer created though controlled architecture polymerization and depicted in Figure
4 demonstrates both an improved peel strength (pounds per linear inch) and shear strength
(minutes) when compared to the randomly crosslinked network depicted in Figure 3.
Non-CAPs
[0100] In certain embodiments, the melt processable, actinic radiation polymerizable and
crosslinkable adhesives of the present subject matter are produced from polymers that
are not controlled architecture polymers, or as referred to herein as "non-CAPs."
Such adhesives are free of controlled architecture polymers.
[0101] In many applications involving non-CAP based adhesives, the polymers are acrylic
or alkyl acrylate polymers.
[0102] The alkyl acrylates and alkyl methacrylates used in the present subject matter include
straight chain alkyl groups, branched chain alkyl groups, or cyclic alkyl groups and,
in many embodiments contain from 1 to about 24 carbon atoms. In particular embodiments,
the alkyl group contains from 1 to about 12 carbon atoms.
[0103] In a particular embodiment, the alkyl acrylate or alkyl methacrylate monomers have
from about 4 to about 8 carbon atoms. Such monomers are generally commercially available
as commodity chemicals and are less expensive than longer chain alkyl acrylates and
methacrylates. They also tend to yield copolymers having a good balance of tack and
peel.
[0104] A representative, but nonlimiting list of alkyl acrylates and alkyl methacrylates
useful in the practice of the present subject matter includes methyl acrylate, ethyl
acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate,
n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, isohexyl acrylate, cyclohexyl
acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, lauryl acrylate,
stearyl acrylate, isobornyl acrylate, and mixtures thereof, as well as the analogous
methacrylate monomers. It will be appreciated, however, that alkyl methacrylates generally
yield copolymers having higher Tg's than their alkyl acrylate counterparts. Therefore,
when alkyl methacrylates are used, they are employed in small quantities only. As
a general rule of thumb, the alkyl methacrylates comprise no more than about 15% of
the total weight of all monomers.
[0105] The non-CAP polymer(s) include one or more reactive functional groups as described
herein in association with the CAPs. However, the one or more reactive functional
groups can be incorporated along the polymer chain or backbone in a non-structured
or random or non-ordered manner.
[0106] Representative and non-limiting examples of ranges of glass transition temperatures
(Tg) for the non-CAP polymers typically are from about -60° C to about -35° C. However,
it will be appreciated that the polymers of the present subject matter can exhibit
Tg's outside of this range such as less than - 60° C and/or greater than -35° C.
[0107] It is also contemplated that the present subject matter may include combinations
or blends of CAPs and non-CAPs.
Methods
[0108] In many embodiments, the present subject matter provides methods of forming an adhesive.
The methods comprise providing a composition including at least one monomer having
one or more ethylenically unsaturated bonds, a first actinic radiation initiator,
and a second actinic radiation initiator, wherein the second initiator is substantially
non-photoactive at activation wavelength(s) of the first initiator. The methods also
comprise at least partially polymerizing the composition by exposing the composition
to radiation having wavelengths corresponding to the activation wavelength(s) of the
first initiator. The methods additionally comprise at least partially crosslinking
the composition to thereby form the adhesive by exposing the composition to radiation
having wavelengths corresponding to the activation wavelength(s) of the second initiator.
In these methods the composition is free of solvents.
[0109] In still other embodiments, the present subject matter provides additional methods
of forming an adhesive. The methods comprise providing a composition including at
least one monomer, a first actinic radiation initiator, and a second actinic radiation
initiator, wherein the second initiator is substantially non-photoactive at activation
wavelength(s) of the first initiator. The methods also comprise at least partially
polymerizing the composition by exposing the composition to radiation having wavelengths
corresponding to the activation wavelength(s) of the first initiator. The methods
additionally comprise at least partially crosslinking the composition to thereby form
the adhesive by exposing the composition to radiation having wavelengths corresponding
to the activation wavelength(s) of the second initiator. At least one of the first
and the second initiators is a polymer having a photoinitiator moiety along the polymer
backbone.
[0110] The present subject matter also provides methods of forming a melt processable, actinic
radiation polymerizable and crosslinkable adhesive. In many embodiments, the methods
utilize controlled architecture polymers that include at least one reactive functional
group. In certain embodiments, at least 80% of the reactive functional groups are
located within terminal ends of the polymer. The methods also comprise providing two
or more initiators as described herein. The methods additionally comprise blending
the polymers, which as noted may be controlled architecture polymers, with the initiators
to thereby form a pre-adhesive composition.
[0111] The present subject matter also provides methods of forming actinic radiation polymerizable
and crosslinkable melt adhesives using non-CAP based polymers as described herein.
In these embodiments, the methods comprise providing nonstructured polymers that include
one or more reactive functional groups. The methods also comprise providing two or
more initiators capable of polymerizing and crosslinking the composition. The methods
also comprise blending the polymers with the initiators to thereby form a pre-adhesive
composition. The methods additionally comprise exposing the composition to actinic
radiation for a time period and at an intensity in a first stage sufficient to at
least partially polymerize the composition. The methods also comprise exposing the
composition for a time period and at an intensity in a second stage sufficient to
crosslink the composition and thereby form the adhesive.
[0112] The present subject matter adhesives or compositions are polymerized and/or crosslinked
by exposure to actinic radiation, and particularly ultraviolet (UV) radiation or near
UV radiation. As previously noted, electron beam radiation can also be used. As will
be appreciated, sufficient exposure to such radiation causes polymerization and/or
crosslinking involving various functional groups incorporated in the polymers and
in certain embodiments the CAPs.
[0113] Use of the two stage methods described herein enable formation of a pre-adhesive
formulation that can be further processed by subsequent or additional exposure to
actinic radiation and particularly UV radiation. Thus, an initial batch or a desired
amount of pre-adhesive can be polymerized or at least partially polymerized in bulk
and then stored or held for later application or coating to a substrate of interest.
[0114] After the adhesive is coated on a substrate at a desired coat weight, the coated
substrate is irradiated with actinic radiation and particularly UV radiation to yield
a crosslinked adhesive and in many embodiments a pressure sensitive adhesive having
high cohesive strength at room and elevated temperatures. A variety of UV light sources
are known, including low, high, and medium pressure mercury lamps, which emit over
a wide range of wavelengths. Most pigmented and unpigmented adhesives can be readily
cured using a medium pressure mercury lamp, which has emission bands ranging from
about 240 to about 410 nanometers. Alternatively, UV sources that emit over a more
narrow range of wavelengths can be used if desired, so long as the emission spectrum
of the source overlaps with the absorption spectrum of the initiator(s) employed within
the adhesive. Where the adhesive is pigmented with titanium dioxide or similar pigments,
the preferred initiator has absorption bands in the near UV region, and a UV source
that emits at least in that region is employed.
[0115] As noted, in particular embodiments, the methods of the present subject matter involve
the use of one or both of the initiators being in the form of polymerizable monomers.
The methods involve incorporation and/or polymerization of the first and/or second
initiators into the polymers constituting the adhesive.
[0116] Figure 5 is a process schematic diagram depicting a representative process and system
10 for producing an adhesive and polymerizing and crosslinking the adhesive in accordance
with the present subject matter. The system 10 generally comprises a dispenser or
heater 12 for introducing one or more adhesives, polymers, and/or monomers via feed
line 14 to a blender or mixer 22. Also provided are additional feed lines 16, 18,
and 20 which can be for selectively metering desired amounts of a first initiator,
a second initiator, and ancillary components or other additives to the mixer 22. It
will be appreciated that the first and/or second initiator can be introduced in the
form of polymerizable monomers which are polymerized with or separately from monomer(s)
that form the adhesive.
[0117] After appropriate mixing of the adhesive, polymers and/or monomers, photoinitiators,
and optional components, the resulting pre-adhesive is directed through line 24 to
a reactor 26 which can be in the form of a tube reactor for example. The reactor 26
can be in a variety of different forms however typically defines an interior region
for receiving adhesive or pre-adhesive. The reactor 26 is configured to allow actinic
radiation such as UV radiation to enter the interior of the reactor from one or more
radiation sources as described herein. The adhesive is directed through the reactor
26 and exposed in a first stage to actinic radiation from UV emitters 28, 30 that
emit UV light or radiation shown as rays 29, 31 for example, having a wavelength corresponding
to an activation wavelength of one of the initiators and typically the first initiator.
The flow rate, i.e., residence time of adhesive in the reactor 26; intensity of the
UV light; and other factors are adjusted to produce a partially or fully polymerized
adhesive exiting the reactor 26 via line 32. Polymerization between monomer(s) primarily
occurs in the reactor 26.
[0118] The adhesive in line 32 may be directly deposited or applied to one or more substrates
on a moving web 42 (typically driven by rotating roller 40) via line 34, or directed
via line 36 to a storage unit 44 for additional processing and/or subsequent application.
[0119] Upon deposition of the adhesive shown in Figure 5 as regions 46, the adhesive typically
on the moving web 42, is irradiated by another UV emitter in a second stage 50 that
directs UV rays 51 upon the regions 46 to crosslink the adhesive. Crosslinked adhesive
52 results.
[0120] In particular embodiments, two or more conventional medium pressure mercury lamps
can be used having spectral emissions from about 240 to about 410 nanometers, and
light intensities of from about 5 to 10 kWatts/m
2. Nonlimiting examples of UV light intensities for processing adhesives of the present
subject matter can range from about 0.1 to about 100 kWatts/m
2, in certain embodiments from 1 to 50 kWatts/m
2, and in particular embodiments from 1 to 20 kWatts/m
2. The coated substrate is carried on a moving web under or near the UV radiation source,
where the web temperature may range from 45° C to 125° C. The dosage of UV radiation
received by the coated adhesive film is controlled by adjusting the UV lamp intensity
and/or the web speed. Nonlimiting examples of time periods for processing adhesives
of the present subject matter are typically less than 60 minutes, more typically less
than 10 minutes, in many embodiments less than 1 minute, and in particular embodiments
less than 10 seconds.
[0121] Upon exposing adhesive to the noted conditions, if the adhesive includes CAPs, the
adhesive then includes an ETLN. As previously described, the ETLN adhesives of the
present subject matter exhibit an array of advantages and benefits and particularly
when compared to non-architecture polymers which produce randomly crosslinked networks.
[0122] Specifically, as shown in Figure 6, a method 60 includes providing a melt adhesive
having (i) a first UV photoinitiator for bulk curing of the adhesive, and (ii) a second
UV photoinitiator for on-web crosslinking of the adhesive. The second photoinitiator
is substantially non-photoactive at activation wavelengths of the first photoinitiator.
This is depicted as one or more operations 65 in Figure 6. The methods also include
at least partially curing the adhesive by irradiating the adhesive with UV light having
wavelengths corresponding to the activation wavelengths of the first photoinitiator.
This is shown as one or more operations 70 in Figure 6. The methods additionally include
applying the at least partially cured adhesive to a surface of interest. And, the
methods include crosslinking the adhesive shown as operation(s) 75 by irradiating
the adhesive with UV light having wavelengths corresponding to the activation wavelengths
of the second photoinitiator, to thereby form the adhesive at 80. It will be appreciated
that the present subject matter includes the use of initiators activated by exposure
to electron beam radiation instead of, or in addition to, either or both of the first
and second UV photoinitiator(s).
[0123] As will be understood, during conversion of the composition(s) of the present subject
matter from a pre-adhesive to a pressure sensitive adhesive, in many embodiments,
the modulus of the composition changes while the glass transition temperature (Tg)
does not change or remains substantially the same.
Optical Filters
[0124] Another aspect of the present subject matter involves selective exposure of UV radiation
having a desired wavelength or range of wavelengths to one or both of the UV photoinitiators
at particular times or process phases. For example, in one embodiment of the present
subject matter, one or more optical filters can be used to selectively filter and/or
block UV radiation of particular wavelength(s). Using this technique, adhesive or
pre-adhesive can be exposed to a UV radiation source that activates the first UV photoinitiator
yet which does not activate the second photoinitiator. In this version of the present
subject matter, one or more optical filters are used to selectively block UV radiation
having wavelength(s) corresponding to the activation wavelength(s) of the second photoinitiator.
The present subject matter also includes the use of optical filters to selectively
filter and/or block particular radiation wavelength(s) that correspond to the activation
wavelength(s) of the first photoinitiator.
[0125] A wide array of materials and equipment can be used to provide the noted optical
filter(s). The optical filter(s) are positioned between the UV radiation source and
the adhesive or pre-adhesive. Referring to Figure 5 again, the one or more optical
filters can be disposed or otherwise positioned between the UV emitter 28 and the
reactor 26 so that the UV radiation 29 passes through the filters. Similarly, one
or more optical filters could be positioned between region(s) 46 and the second stage
50. In many embodiments, the optical filters include particular polymeric layers,
lenses, and/or films that are formulated to allow passage of certain wavelengths and
block passage of other wavelengths. Nonlimiting examples of such materials include
polycarbonates such as those commercially available under the LEXAN® designation,
certain polyethylene terephthalates, certain polymethyl methacrylates (PMMAs), and
combinations thereof. It is also contemplated to utilize one or more dichroic glasses
as the optical filters described herein. It will be understood that the present subject
matter is not limited to any of these particular materials. Instead, the subject matter
includes a wide array of materials and assemblies for selectively filtering and/or
enabling passage of electromagnetic radiation having desired wavelength(s) to the
adhesive or pre-adhesive.
[0126] The optical filter(s) can be configured to block or otherwise prevent passage of
electromagnetic radiation and in particular UV radiation having particular wavelength(s).
In many embodiments, the optical filters block passage of UV radiation having wavelength(s)
corresponding to the activation wavelength(s) of the second photoinitiator. As previously
noted, in certain embodiments of the present subject matter the activation wavelengths
of the second photoinitiator are within a range of from 100 nm to 500 nm, and particularly
from 200 nm to 375 nm.
[0127] The optical filter(s) can be configured such that they can be selectively positioned
between one or more light sources and the adhesive or process component(s) containing
the adhesive or pre-adhesive such as a reactor. The optical filter(s) can also be
configured so that the filter(s) can be moved to thereby allow passage of light in
an unfiltered or unblocked manner.
[0128] If multiple light sources are used, the present subject matter includes the use of
optical filter(s) associated with some or all of the light sources. The present subject
matter includes a wide array of process components and system configurations.
Articles
[0129] The present subject matter provides a wide array of articles that include the noted
compositions, pre-adhesives, and/or adhesives. Examples of such articles include adhesive
tapes including double sided and single sided tapes; label stock; label constructions;
packaging products and assemblies including food packages, packaging for household
goods and industrial goods and particularly reclosable packages; and other items.
[0130] Figure 7 illustrates a tape article 100 in accordance with an embodiment of the present
subject matter. The tape article 100 is shown in a roll form, however, it will be
appreciated that the tape could be in a flat, sheet, or Z-fold form. The tape article
100 generally includes a substrate 110 defining a first face 112 and an oppositely
directed second face 114. The tape 100 includes a layer or region of an adhesive as
described herein disposed on one or both faces 112, 114. One or more release liners
and/or low surface energy coatings can be used as described in greater detail herein.
[0131] Figure 8 is a schematic cross sectional view of a tape 100A comprising a substrate
110 defining a first face 112 and an oppositely directed second face 114. The tape
100A also comprises a layer or region of an adhesive 120 disposed on one of the faces
such as for example face 114. One or more low surface energy coatings can be disposed
on the face 112 of the substrate 110.
[0132] Figure 9 is a schematic cross sectional view of a tape 100B comprising a substrate
110 defining a first face 112 and an oppositely directed second face 114. The tape
100B also comprises a layer or region of an adhesive 120 disposed on one of the faces
such as for example face 114. The tape 100B also comprises a release liner 130 covering
the adhesive 120. One or more low surface energy coatings can be disposed on the face
112 of the substrate 110.
[0133] Figure 10 is a schematic cross sectional view of a tape 100C comprising a substrate
110 defining a first face 112 and an oppositely directed second face 114. The tape
100C also comprises a first layer or region of an adhesive 120 disposed on one of
the faces such as for example face 114. The tape 100B also comprises a second layer
or region of an adhesive 125 disposed on the face 112 of the substrate 110.
[0134] Figure 11 is a schematic cross sectional view of a tape 100D comprising a substrate
110 defining a first face 112 and an oppositely directed second face 114. The tape
100D also comprises a first layer or region of an adhesive 120 disposed on one of
the faces such as for example face 114. The tape 100D also comprises a second layer
or region of an adhesive 125 on the face 112. The tape 100D also comprises a first
release liner 130 covering the adhesive 120. And, the tape 100D additionally comprises
a second release liner 135 covering the adhesive 125.
[0135] Figure 12 is a schematic cross sectional view of a sealing, closure, or reclosure
assembly 200 in accordance with the present subject matter. This assembly comprises
a first substrate 210 defining a first substrate face 212, a second substrate 230
defining a second substrate face 214, and one or more layers or regions of an adhesive
220 defining an adhesive face 222. The adhesive 220 is disposed on one or both substrate
faces 212, 214. The adhesive 220 serves to seal and/or adhere the substrates 210,
230 together upon contact between the adhesive face 222 and the substrate face 212.
As will be understood, the adhesive 220 is any of the adhesives described herein.
The assembly 200 can be utilized in association with and/or incorporated in a wide
array of packaging products including for example food packages, packages for household
goods, industrial goods packages, and in particular recloseable packages.
[0136] The adhesive layer may have a thickness as desired for a particular purpose or intended
use. In one embodiment, the adhesive layer may have a thickness from about 10 to about
125, or from about 10 to about 75, or from about 10 to about 50 microns. In one embodiment,
the coat weight of the adhesive may be in the range of about 10 to about 50 grams
per square meter (gsm), and in one embodiment about 20 to about 35 gsm.
[0137] Release liners for use in the present subject matter may be those known in the art
or those later discovered. In general, suitable release liners include, but are not
limited to, polyethylene coated papers with a commercial silicone release coating,
polyethylene coated polyethylene terephthalate films with a commercial silicone release
coating, or cast polypropylene films that can be embossed with a pattern or patterns
while making such films, and thereafter coated with a commercial silicone release
coating. An exemplary release liner is kraft paper which has a coating of low density
polyethylene on the front side with a silicone release coating and a coating of high
density polyethylene or polypropylene on the back side. Other release liners known
in the art are also suitable as long as they are selected for their release characteristics
relative to the pressure sensitive adhesive chosen for use in the adhesive article,
that is, the adhesive will have a greater affinity for the face stock than the liner.
[0138] As previously noted, one or more low surface energy coatings can be used in the articles
utilizing the adhesives described herein. For example, for rolled tape products it
may be desirable to provide a coating of a low surface energy agent along a rear face
of a substrate or tape component that contacts the adhesive. Nonlimiting examples
of low surface energy coatings include silicone agents, polypropylene or other polyolefins,
certain fluorocarbons, and certain fatty acid esters.
[0139] A benefit of particular adhesives of the present subject matter involves maintenance
of performance criteria upon continued exposure to UV radiation. For example, a disadvantage
of many conventional UV cured, randomly crosslinked adhesive networks is that additional
UV exposure results in additional crosslinking. This may in turn result in undesirable
changes in the adhesive and/or its performance. Specifically, this may be undesirable
for clear or transparent labels that are UV printed downstream. In contrast, many
embodiments of the present subject matter adhesives do not exhibit performance changes
upon additional UV exposure.
Additional Aspects
[0140] Figure 13 schematically illustrates an apparatus for polymerizing or crosslinking
adhesives by exposure to actinic radiation using one or more light emitting probes.
Specific wavelengths of radiation emitted at specific angles and heights relative
to an upper surface of an adhesive or pre-adhesive contained within the apparatus
are used to achieve varying polymer properties. Figure 13 shows three of four positions
of irradiation: surface, angled surface, sub-surface, and angled sub-surface. Probes
can be attached to the side, top, or bottom of a reaction vessel and are held in place
via pressure rated sealing and locking collars. This provides further flexibility
to the penetration depth of each probe. A typical configuration for individual probes
is one in which each probe comprises a pressure rated light tube, LED emitter, and
a Class 1/Division 1 enclosure with integrated heat sink. The light controller/driver
is located remotely. The probe is constructed with a smoothed, polished interior wall
that reflects radiation from the source and emits the radiation through the tip of
the probe within the reaction vessel. Materials that are transparent to the radiation
wavelengths are used at the probe's tip. Nonlimiting examples of such materials include
glass, quartz, sapphire, and similar materials. In many embodiments, the complete
apparatus is certified to meet or exceed pressure and temperature ratings of the chosen
reaction vessel. In addition to LED, other light sources can be considered along with
other ancillary apparatus components such as power source, cooling provisions and
the like.
[0141] Specifically, referring to Figure 13, an apparatus 300 for polymerizing and/or crosslinking
an adhesive or pre-adhesive composition is shown. The apparatus comprises a reaction
vessel 320 defining an interior chamber 322 for the composition. The vessel 320 typically
includes stirring or mixing provisions 340, one or more drain ports 350, and associated
valving 352 to govern entry and exit of flow(s) to the vessel 320. An optional heating
and/or cooling jacket 370 may be provided along exterior regions of the vessel 320.
The apparatus 300 also comprises one or more probe assemblies 310 engaged with the
reaction vessel 320 via collar(s) 330. The collar 330 provides access to the interior
chamber 322 of the vessel 320 and is located along an upper region of the vessel 320
typically within a top wall of the vessel 320. The collar 320 includes provisions
for releasably engaging a probe assembly 310 and supporting the probe assembly relative
to the vessel 320. The probe assembly 310 includes an emitter 312, a light tube 314
extending from the emitter, optional heat sink provisions 318 associated with the
emitter 312, and adjustable positioning provisions 316. The light tube 314 defines
a distal end 315 opposite the emitter 312. In many embodiments, a probe assembly 310
is disposed relative to the reaction vessel 320 such that the emitter 312 is positioned
above the vessel 320, and the light tube 314 extends into the interior chamber 322
of the vessel 320 through the collar 330. The adjustable positioning provisions 316
are engaged or associated with the light tube 314 and serve to govern and/or maintain
a desired position of the light tube 314 within the chamber 322. Figure 13 depicts
various positions of the light tube 314 relative to the vessel 320 and specifically,
an upper surface 302 of an adhesive or pre-adhesive composition contained within the
vessel 320. For example, probe assembly 310A includes an emitter 312A, a light tube
314A extending into the interior chamber 322 of the vessel 320, and adjustable positioning
provisions 316A. Probe assembly 310A is depicted in an angled sub-surface position
as the light tube 314A is at a non-vertical orientation and the distal end 315A of
the light tube 314A is below the upper surface 302 of the composition contained within
the vessel 320. Probe assembly 310B includes an emitter 312B, a light tube 314B extending
into the chamber 322, and adjustable positioning provisions 316B. Probe assembly 310B
is depicted in sub-surface position as the light tube 314B is at a vertical orientation
and the distal end 315B of the light tube 314B is below the upper surface 302. Probe
assembly 310C includes an emitter 312C, a light tube 314C extending into the chamber
322, and adjustable positioning provisions 316C. Probe assembly 310C is shown in an
angled surface position as the light tube 314C is at a non-vertical orientation and
the distal end 315C of the light tube 314C is above the upper surface 302. As will
be appreciated, a surface position for a probe assembly corresponds to a light tube
oriented at a vertical position and having a distal end of the light tube positioned
above the upper surface.
[0142] The apparatus 300 can include a single probe assembly or multiple probe assemblies.
And, the probe assemblies can be located proximate one another as shown in Figure
13, or the probe assemblies can be located along different regions of the vessel such
as one or two or more located along a top region, and one or two or more located along
side region(s) of the vessel.
[0143] The emitter 312 of a probe assembly 310 typically includes one or more emitter(s)
of actinic radiation such as a light source. The emitter 312 can optionally include
heat dissipating provisions such as an integrated heat sink 318 located along exterior
region(s) of the emitter 312. As will be understood each emitter is in communication
with a signal and/or power unit 360. One or more signal/power communication(s) 362
extend between the emitter 312 and the signal/power unit 360.
[0144] In certain embodiments, the interior wall of a light tube, such as light tubes 314A,
314B, and/or 314C, provides a smooth, polished surface that promotes reflection of
light emitted from the emitter. And, in many embodiments, one or more transparent
covers 317 are provided at or proximate the distal end 315 of the light tube 314.
As noted, the cover is transparent or substantially transparent to the passage of
light emitted from the emitter and reflected along a length or length portion of the
light tube. The term "substantially transparent" as used herein refers to the cover
having optical properties that enable at least 90% of light emitted from the emitter
312 and reflected along the light tube, to pass through the cover 317.
[0145] An advantage of mounting a probe in a nozzle in the top (also known as "head of the
vessel") is that the probe can be removed without draining/releasing the contents
of the vessel. Another advantage of mounting a probe above the upper surface 302 is
that on the outside vertical walls and bottom walls of the vessel, such walls are
typically covered with a jackets (i.e., "welded half-pipe") to provide cooling or
heating the contents via thermal conduction. For example, to cool an exothermic reaction,
cold water is typically circulated through a half-pipe jacket. The presence of the
jacket for cooling limits the amount of surface area available and complicates the
installation of the probe through the side-walls and bottom wall.
[0146] Another mode of introducing actinic radiation via a probe is through a port, collar,
or nozzle incorporated into the vessel below the surface of the liquid, either via
the side wall or the bottom wall of the vessel (see Figure 14). This is in contrast
to Figure 13, in which the collar is mounted on the top wall of the vessel. An advantage
of mounting the probe in the bottom wall is that for any fillage of the vessel, the
probe is always submersed. The distance between the probe tip and the liquid is essentially
zero, independent of batch size.
[0147] Specifically, referring to Figure 14, another version of the apparatus 300 previously
described in association with Figure 13 is shown. In this version, a probe assembly
310D is located along a side wall of the reaction vessel 320, and a probe assembly
310E is located along a bottom wall of the vessel 320. Each probe assembly 310D and
310E is engaged with the vessel 320 by a corresponding collar 330D and 330E. In the
particular version shown in Figure 14, the distal ends 315D and 315E of the light
tubes 314D and 314E are flush or substantially flush with an interior surface of the
vessel wall. As previously described, transparent covers 317 are typically located
at the light tube distal ends, thus, covers 317D and 317E are substantially flush
with the interior wall of the vessel 320.
[0148] Yet another mode is to irradiate the contents of the reactor using a sight glass
built into the side vessel, instead of installing a probe through a nozzle or port
(see Figure 15). The sight glass is typically flush with the side wall of the vessel.
An advantage of having a sight glass flush with the side wall of the vessel is that
some vessels have agitator designs that sweep the inside wall of the vessel at a small
gap (akin tolerance or distance). A sweeping agitator blade helps promote heat transfer
in viscous materials. Also, if the light is causing a reaction to occur near the glass-product
interface, the wiping agitator blade promotes the mixing of viscous, reacted product
in the irradiated zone with lower viscosity material outside the irradiated zone.
[0149] Specifically, Figure 15 illustrates another version of the apparatus 300. This figure
depicts additional aspects of the stirring or mixing provisions 340. As will be understood,
many such provisions 340 include a power unit for rotating a shaft generally extending
into the interior chamber 322 of the vessel 320. The provisions 340 typically include
one or more blades or mixing elements extending from the shaft. In this version, the
reaction vessel includes one or more sight glasses 380 incorporated within wall region(s)
of the vessel. The sight glass(es) provides visual access to the interior of the vessel.
For example, in the version of Figure 15, a plurality of sight glasses 380 are provided,
i.e., sight glasses 380A, 380B, and 380C. One or more emitter(s) such as emitter 312F
can be positioned adjacent a sight glass such as sight glass 380A. Emission of light
from the emitter 312F passes through the sight glass 380A to irradiate the contents
of the vessel 320. In addition or alternatively, one or more emitter(s) such as emitter
312G can be positioned adjacent a sight glass such as sight glass 380C, and a light
tube such as light tube 314G can be used to direct light from the emitter 312G to
the sight glass 380C for irradiation into the chamber 322 of the vessel 320. One or
more transparent covers can be used, however, such is likely not necessary. As will
be appreciated, it is desired for many applications that the sight glass is transparent
or substantially transparent to passage of light emitted from the emitter.
[0150] Still another mode of introducing radiation is to mount a LED or other light source
onto a baffle attached to the reactor wall as depicted in Figure 16. In this vessel
type, the contents of the vessel are agitated by a pitched blade turbine. The primary
function of the baffle is to divert flow away from the wall of the vessel. If sufficiently
strong, the enclosure of the light source could also function as a baffle in addition
to being the light source. Alternatively, the light source can be mounted on the front
side of the baffle with respect to the rotation of the liquid due to the agitator
blade. In all these methods, the irradiated material in front of the source would
be constantly renewed to allow reacted viscous material to be thoroughly mixed into
the overall reaction mass.
[0151] Specifically, referring to Figure 16, an apparatus 300 is shown having stirring or
mixing provisions 340 in the form of a pitched blade turbine. One or more emitters
312 are incorporated in a stationary baffle 390 that is affixed within the interior
chamber 322 of the vessel 320. One or more supports 392 attached to the vessel wall
can be used to affix the baffle 390 within the vessel 320. It is also contemplated
that the baffle(s) can extend from support(s) extending through collars in the wall(s).
Although the present subject matter includes baffle(s) 390 that emit light in all
directions from the baffle, in certain versions a uni-directional or substantially
so, light emission configuration is used. Typically, such baffles emit light from
a single face of the baffle. That is, the uni-directional light emission baffle 390
is positioned within the interior chamber 322 of the vessel 320 such that light emitted
from the baffle 390 is directed toward approaching flow(s) of composition resulting
from movement of the blade(s). However, it will be understood that the present subject
matter includes versions in which the baffle(s) emits light directed toward flow(s)
of composition traveling away from the baffle. The baffle(s) can be self-contained
and include batteries and electronics for powering the emitter(s), and/or receive
signals and/or power remotely. Although a pitched blade turbine is preferred for certain
applications, the present subject matter includes other types of stirring/mixing provisions.
[0152] An advantage of subsurface irradiance is that the reaction zone starts immediately
at the probe tip and penetrates a certain distance defined as the "penetration depth".
The "penetration depth" depth depends upon optical density and on the nature of the
material, the applied irradiance, the spectral output, and the photoinitiator and
its concentration. If the light source is positioned above the surface and particulate(s)
exist in the headspace above the liquid, the particulate matter may interact with
the incoming light. In particular, if liquid from the reaction mass is dispersed into
the vapor space and forms an aerosol, then polymer may form in the vapor phase. This
is undesirable because the reaction is no longer homogeneous and also fouls the reactor
headspace and may foul the optic interface and attenuate the irradiation. Also, the
operator can not view the reaction as well with a dirty sight glass. Also, clean up
of the vessel is difficult after the reaction.
[0153] Many other benefits will no doubt become apparent from future application and development
of this technology.
[0154] All patents, applications, standards, and articles noted herein are hereby incorporated
by reference in their entirety.
[0155] The present subject matter includes all operable combinations of features and aspects
described herein. Thus, for example if one feature is described in association with
an embodiment and another feature is described in association with another embodiment,
it will be understood that the present subject matter includes embodiments having
a combination of these features.
[0156] As described hereinabove, the present subject matter solves many problems associated
with previous strategies, systems and/or compositions. However, it will be appreciated
that various changes in the details, materials and arrangements of components, which
have been herein described and illustrated in order to explain the nature of the present
subject matter, may be made by those skilled in the art without departing from the
principle and scope of the claimed subject matter, as expressed in the appended claims.
[0157] The present invention further relates to the following items:
- 1. A method of forming an adhesive, the method comprising:
providing a composition including at least one monomer having one or more ethylenically
unsaturated bonds, a first actinic radiation initiator, and a second actinic radiation
initiator, wherein the second initiator is substantially non-photoactive at activation
wavelength(s) of the first initiator;
at least partially polymerizing the composition by exposing the composition to radiation
having wavelengths corresponding to the activation wavelength(s) of the first initiator;
at least partially crosslinking the composition to thereby form the adhesive by exposing
the composition to radiation having wavelengths corresponding to the activation wavelength(s)
of the second initiator;
wherein the composition is free of solvents.
- 2. The method of item 1 whereby the at least partially polymerizing the composition
is performed by irradiating the composition with UV radiation.
- 3. The method of item 1 whereby the at least partially polymerizing the composition
is performed by irradiating the composition with electron beam radiation.
- 4. The method of item 1 whereby the at least partially crosslinking the composition
is performed by irradiating the composition with UV radiation
- 5. The method of item 1 whereby the at least partially crosslinking the composition
is performed by irradiating the composition with electron beam radiation.
- 6. The method of any one of items 1-5 wherein the first initiator is a polymerizable
initiator.
- 7. The method of any one of items 1-6 wherein the second initiator is a polymerizable
initiator.
- 8. The method of any one of items 1-7 wherein the monomer having one or more ethylenically
unsaturated bonds is an acrylate monomer.
- 9. The method of any one of items 1-8 whereby the at least partially polymerizing
the composition forms a pre-adhesive composition that includes controlled architecture
polymers including a reactive functional group.
- 10. The method of item 9 wherein the controlled architecture polymers exhibit an apportionment
ratio of the reactive functional group between two blocks of the polymer within a
range of from 1.1:1 to 10,000:1.
- 11. An adhesive formed by any of the methods of items 1-10.
- 12. An article comprising the adhesive of item 11.
- 13. A method of forming an adhesive, the method comprising:
providing a composition including at least one monomer, a first actinic radiation
initiator, and a second actinic radiation initiator, wherein the second initiator
is substantially non-photoactive at activation wavelength(s) of the first initiator;
at least partially polymerizing the composition by exposing the composition to radiation
having wavelengths corresponding to the activation wavelength(s) of the first initiator;
at least partially crosslinking the composition to thereby form the adhesive by exposing
the composition to radiation having wavelengths corresponding to the activation wavelength(s)
of the second initiator;
wherein at least one of the first and the second initiators is a polymer having a
photoinitiator moiety along the polymer backbone.
- 14. The method of item 13 whereby the at least partially polymerizing the composition
is performed by irradiating the composition with UV radiation
- 15. The method of item 13 whereby the at least partially polymerizing the composition
is performed by irradiating the composition with electron beam radiation.
- 16. The method of item 13 whereby the at least partially crosslinking the composition
is performed by irradiating the composition with UV radiation.
- 17. The method of item 13 whereby the at least partially crosslinking the composition
is performed by irradiating the composition with electron beam radiation.
- 18. The method of any one of items 13-17 whereby the at least partially polymerizing
the composition forms a pre-adhesive composition that includes controlled architecture
polymers including a reactive functional group.
- 19. The method of item 18 wherein the controlled architecture polymers exhibit an
apportionment ratio of the reactive functional group between two blocks of the polymer
within a range of from 1.1:1 to 10,000:1.
- 20. An adhesive formed by any of the methods of items 13-19.
- 21. An article comprising the adhesive of item 20.
- 22. A composition comprising:
at least one monomer having one or more ethylenically unsaturated bonds;
a first actinic radiation initiator for at least partially polymerizing the at least
one monomer to form a pre-adhesive, the first initiator being activated at a first
activation wavelength(s);
a second actinic radiation initiator for at least partially crosslinking the pre-adhesive,
the second initiator being activated at a second activation wavelength(s) and the
second initiator being substantially non-photoactive at the first activation wavelength(s).
- 23. The composition of item 22 wherein the first initiator is activated by exposure
to UV radiation.
- 24. The composition of any one of items 22-23 wherein the first initiator is activated
by exposure to electron beam radiation.
- 25. The composition of any one of items 22-24 wherein the second initiator is activated
by exposure to UV radiation.
- 26. The composition of any one of items 22-25 wherein the second initiator is activated
by exposure to electron beam radiation.
- 27. The composition of any one of items 22-26 wherein upon activation of the first
initiator to form the pre-adhesive, the pre-adhesive exhibits a viscosity within a
range of from 1,000 cps to 80,000 cps at a temperature within a range of from 110°
C to 180° C.
- 28. The composition of item 27 wherein the pre-adhesive exhibits a viscosity within
a range of from 30,000 cps to 40,000 cps at a temperature within a range of from 120°
C to 140° C.
- 29. The composition of item 27 wherein the pre-adhesive exhibits a viscosity within
a range of from 40,000 cps to 50,000 cps at a temperature within a range of from 120°
C to 140° C.
- 30. The composition of item 27 wherein the pre-adhesive exhibits a viscosity within
a range of from 1,000 cps to 15,000 cps at a temperature within a range of from 110°C
to 130°C.
- 31. The composition of any one of items 22-30 wherein the at least one monomer is
an acrylate monomer.
- 32. The composition of any one of items 22-31 further comprising at least one component
selected from the group consisting of pigments, tackifiers, plasticizers, fillers,
diluents, inhibitors, and combinations thereof.
- 33. An article comprising the composition of any one of items 22-32.
- 34. An acrylate melt processable pre-adhesive composition comprising:
at least one acrylate polymer;
an actinic radiation initiator for at least partially crosslinking the polymer, the
initiator being a photoinitiator moiety along the polymer backbone;
wherein the pre-adhesive composition prior to activation of the initiator exhibits
a viscosity within a range of from 1,000 cps to 80,000 cps at a temperature within
a range of from 110° C to 180° C.
- 35. The composition of item 34 wherein the pre-adhesive exhibits a viscosity within
a range of from 30,000 cps to 40,000 cps at a temperature within a range of from 120°
C to 140° C.
- 36. The composition of item 34 wherein the pre-adhesive exhibits a viscosity within
a range of from 40,000 cps to 50,000 cps at a temperature within a range of from 120°C
to 140°C.
- 37. The composition of item 34 wherein the pre-adhesive exhibits a viscosity within
a range of from 1,000 cps to 15,000 cps at a temperature within a range of from 110°C
to 130°C.
- 38. The composition of any one of items 34-37 wherein the composition includes at
least 95% solids.
- 39. The composition of any one of items 34-38 wherein upon exposure to actinic radiation
corresponding to the activation wavelengths of the initiator, the composition is a
pressure sensitive adhesive.
- 40. The composition of any one of items 34-39 wherein the at least one acrylate polymer
includes alkyl acrylate polymers.
- 41. The composition of any one of items 34-40 wherein the acrylate polymer is a controlled
architecture polymer including a reactive functional group.
- 42. The composition of item 41 wherein the controlled architecture polymer exhibits
an apportionment ratio of the reactive functional group between two blocks of the
polymer within a range of form 1.1:1 to 10,000:1.
- 43. The composition of item 41 wherein the controlled architecture polymer has a molecular
weight within a range of from 10,000 to 300,000.
- 44. The composition of item 41 wherein the controlled architecture polymer has a polydispersity
value less than 4.0.
- 45. An article comprising the composition of any one of items 34-44.
- 46. An apparatus for polymerizing and/or crosslinking an adhesive or pre-adhesive
composition, the apparatus comprising:
a reaction vessel defining an interior chamber and including at least one collar providing
access to the interior chamber;
at least one probe assembly supported by the collar, the probe assembly including
(i) an emitter for emitting light that polymerizes and/or crosslinks the composition,
(ii) a light tube extending from the emitter and at least partially disposed within
the interior chamber of the reaction vessel, (iii) adjustable positioning provisions
for governing position of the light tube within the interior chamber of the reaction
vessel, and (iv) a cover disposed at a distal end of the light tube, wherein the cover
is transparent or substantially transparent to passage of light emitted from the emitter.
- 47. The apparatus of item 46 wherein the probe assembly is positionable to at least
one position selected from the group consisting of a surface position, an angled surface
position, a sub-surface position, and an angled sub-surface position.
- 48. The apparatus of item 46 wherein the apparatus comprises a single probe assembly.
- 49. The apparatus of item 46 wherein the apparatus comprises multiple probe assemblies.
- 50. The apparatus of item 46 wherein the collar and at least one probe assembly are
located along a top wall of the reaction vessel.
- 51. The apparatus of item 46 wherein the collar and at least one probe assembly are
located along a side wall of the reaction vessel.
- 52. The apparatus of item 46 wherein the collar and at least one probe assembly are
located along a bottom wall of the reaction vessel.
- 53. The apparatus of any one of items 46-52 wherein the vessel further includes mixing
provisions.
- 54. An apparatus for polymerizing and/or crosslinking an adhesive or pre-adhesive
composition, the apparatus comprising:
a reaction vessel defining an interior chamber and at least one sight glass incorporated
in a wall of the vessel and providing visual access to the interior chamber;
at least one probe assembly adjacent the sight glass, the probe assembly including
an emitter for emitting light that polymerizes and/or crosslinks the composition,
the probe assembly positioned such that light emitted from the emitter is directed
to the sight glass and passes into the interior chamber of the reaction vessel;
wherein the sight glass is transparent or substantially transparent to passage of
light emitted from the emitter.
- 55. The apparatus of item 54 wherein the probe assembly further includes a light tube
disposed between the sight glass and the emitter.
- 56. The apparatus of item 54 wherein the sight glass is located along a side wall
of the reaction vessel.
- 57. The apparatus of any one of items 54-56 wherein the vessel further includes mixing
provisions.
- 58. An apparatus for polymerizing and/or crosslinking an adhesive or pre-adhesive
composition, the apparatus comprising:
a reaction vessel defining an interior chamber, the vessel including mixing provisions
having at least one blade;
at least one baffle disposed within the interior chamber of the reaction vessel, the
baffle including at least one emitter for emitting light that polymerizes and/or crosslinks
the composition.
- 59. The apparatus of item 58 wherein the baffle is a uni-directional light emission
baffle having a single face that emits light.
- 60. The apparatus of item 59 wherein the baffle is oriented within the interior chamber
such that upon operation of the mixing provisions, the at least one blade moves toward
the single face of the baffle that emits light.